[Federal Register: December 5, 2006 (Volume 71, Number 233)]
[Proposed Rules]
[Page 70483-70492]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr05de06-14]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants; 90-Day Finding on
a Petition To List the Tricolored Blackbird as Threatened or Endangered
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of 90-day petition finding.
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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), announce a
90-day finding on a petition to list the tricolored blackbird (Agelaius
tricolor) as threatened or endangered under the Endangered Species Act
of 1973, as amended. We find that the petition does not present
substantial scientific or commercial information indicating that
listing the tricolored blackbird may be warranted. Therefore, we will
not be initiating a status review in response to this petition. We ask
the public to submit to us any new information that becomes available
concerning the status of, or threats to, the tricolored blackbird or
its habitat at any time.
DATES: The finding announced in this document was made on December 5,
2006. You may submit new information concerning this species for our
consideration at any time.
ADDRESSES: The complete file for this finding is available for public
inspection, by appointment, during normal business hours at the
Sacramento Fish and Wildlife Office, U.S. Fish and Wildlife Service,
2800 Cottage Way, Room W-2605, Sacramento, California 95825-1846. New
information, materials, comments, or questions concerning this species
may be submitted to us at any time.
FOR FURTHER INFORMATION CONTACT: Susan Moore, Field Supervisor or
Arnold Roessler, Listing Branch Chief of the Sacramento Fish and
Wildlife Office (see ADDRESSES), by telephone at (916) 414-6600, or by
facsimile to (916) 414-6712. Persons who use a telecommunications
device for the deaf (TDD) may call the Federal Information Relay
Service (FIRS) at 800/877-8339, 24 hours a day, 7 days a week.
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(A) of the Endangered Species Act of 1973, as
amended (Act) (16 U.S.C. 1531 et seq.), requires that we make a finding
on whether a petition to list, delist, or reclassify a species presents
substantial scientific or commercial information indicating that the
petitioned action may be warranted. We are to base this finding on
information provided in the petition, supporting information submitted
with the petition, and information otherwise available in our files at
the time we make the determination. To the maximum extent practicable,
we are to make this finding within 90 days of our receipt of the
petition, and the finding is to be published in the Federal Register.
This finding summarizes information included in the petition and
information available to us at the time of the petition review. A 90-
day finding under section 4(b)(3)(A) of the Act and section 424.14(b)
of our regulations is limited to a determination of whether the
information in the petition meets the ``substantial information''
threshold. Substantial information is ``that amount of information that
would lead a reasonable person to believe that the measure proposed in
the petition may be warranted'' (50 CFR 424.14(b)).
Previous Federal Action
In 1990, the California Department of Fish and Game (CDFG) added
the tricolored blackbird to its list of Bird Species of Special
Concern. In 1991 the Yolo Chapter of the National Audubon Society
submitted a petition to the Service and to the California Fish and Game
Commission to list the tricolored blackbird as a threatened or
endangered species. Researchers (Hamilton et al. 1995, p. 7) working on
the species in 1992 found that the population had increased from the
late 1980s; thus, the petitioners withdrew their petition based on new
information that the population numbers had increased. The Service
included this species as a candidate (Category 2) for Federal listing
as either threatened or endangered in the 1991 and 1994 Candidate
Notice of Review (CNOR) (59 FR 58981, p. 58990, issued November 15,
1994). Category 2 status included those taxa for which information in
the Service's possession indicated that a proposed listing rule was
possibly appropriate, but for which sufficient data on biological
vulnerability and threats were not available to support a proposed
rule. In the CNOR published on February 28, 1996, the Service announced
a revised list of plant and animal taxa that were regarded as
candidates for possible addition to the List of Threatened and
Endangered Species (61 FR 7595). The revised candidate list included
only former Category 1 species. All former Category 2 species were
dropped from the list in order to reduce confusion about the
conservation status of these species, and to clarify that the Service
no longer regarded these species as candidates for listing. Since the
tricolored blackbird was a Category 2 species, it was no longer
recognized as a candidate species as of the February 28, 1996, CNOR.
The tricolored blackbird is now considered a U.S. Fish and Wildlife
Service Bird of Conservation Concern (USFWS 2002). This designation is
a result of mandates required through the Fish and Wildlife
Conservation Act, which in part requires the Service to identify
nongame migratory bird species that, without additional conservation
actions, are likely to become candidates for listing under the Act. One
of the goals of identifying species of conservation concern is to draw
attention to the
[[Page 70484]]
species in greatest need of conservation action and to focus funding
and efforts on conserving the species and preclude the need for
listing.
On April 8, 2004, we received a petition to list the tricolored
blackbird as a threatened or endangered species from the Center for
Biological Diversity (Center for Biological Diversity 2004). The
petitioner also requested an emergency listing of the species. The
submission clearly identified itself as a petition and included the
requisite identification information of the petitioner, as required in
50 CFR 424.14(a). In our May 25, 2004, response letter to the
petitioner, we said that we had reviewed the petition and determined
that an emergency listing was not warranted, and that because of other
court-ordered listing and critical habitat actions and settlements, we
would not be able to otherwise address the petition to list the
tricolored blackbird at that time, but would complete the action when
workload and funding allowed.
On July 15, 2005, we received a 60-day notice of intent to sue
filed by the Center for Biological Diversity for lack of response to
the petition to list the tricolored blackbird. On February 13, 2006,
the Center for Biological Diversity filed a complaint for declaratory
judgment and injunctive relief in Federal District Court for the
Northern District of California (Center for Biological Diversity v.
Norton et al., No. C-06-0928), for our failure to issue a mandatory 90-
day finding on the petition to list the tricolored blackbird. On May
11, 2006, we reached an agreement with the plaintiff to complete the
90-day finding by December 6, 2006, and if substantial, to complete the
12-month finding by October 18, 2007. This notice constitutes the 90-
day finding for the April 8, 2004, petition to list the tricolored
blackbird.
Species Information
Description and Taxonomy
The tricolored blackbird (Agelaius tricolor) is a medium-sized
blackbird species in which males and females differ in plumage, size,
and behavior. Adult male plumage is entirely black with a blue gloss in
full sunlight. Adult males also have white and red wing plumage, are
generally larger than females, and perform a display when breeding
(Beedy and Hamilton 1999, pp. 1, 10). Immature male plumage is duller
black than adult male plumage and is mottled with gray, eventually
becoming mostly dull black with mixed black shoulder patch (Beedy and
Hamilton 1999, p. 2). Adult female plumage is primarily black, with
grayish streaks. The chin and throat are relatively whitish, rarely
with faint pinkish or peach wash and the shoulder patch is small and
reddish. Immature female plumage is similar to that of the adult
female, except the reddish shoulder patch is absent (Beedy and Hamilton
1999, p. 2). Individuals range from 18 to 24 centimeters (cm) (7 to 9
inches (in)) in length, and from 40 to 70 grams (g) (1 to 2 ounces
(oz)) in body mass, depending on gender and season (Beedy and Hamilton
1999, p. 2).
The tricolored blackbird is a highly colonial species and forms the
largest breeding colonies of any North American passerine (perching)
bird species (Orians and Collier 1962, p. 450; Cook and Toft 2005, p.
74). Breeding colonies can attract thousands of birds to a single site.
During a 1931-1936 study, Neff (1937, pp. 75, 76) described locating a
colony of tricolored blackbirds in 1934 that was estimated to have more
than 200,000 nests. If we take the number of nests reported, and
multiply by 1.5 (mean estimated sex ratio of 2 females per male), we
can calculate an estimated number of breeding adults (Orians 1961a, pp.
300, 308). Using this calculation, we estimate that Neff (1937, pp. 75,
76) documented about 300,000 breeding adults in the one colony.
However, a breeding colony can also contain as few as six nests (about
nine breeding adults), which Neff (1937, p. 79) described finding in
1932 in Solano County. The highly synchronized and colonial breeding
behavior of the tricolored blackbird may have adapted to exploit a
changing environment where the locations of secure nesting habitat and
plentiful food supplies were variable from year to year (Orians 1961a,
pp. 297, 305, 306; Orians and Collier 1962, p. 456; Payne 1969, p. 9).
Habitat
Breeding
Tricolored blackbirds have three basic requirements in selecting a
breeding colony site: (1) Open and accessible water; (2) a protective
nesting substrate, such as flooded, spiny, or thorny vegetation; and
(3) a suitable foraging area within a few kilometers of the nesting
site to provide adequate food such as insects (Hamilton et al. 1995, p.
25; Beedy and Hamilton 1997, p. 4).
Neff (1937, pp. 67, 73) documented that the majority of tricolored
blackbird breeding colony sites he observed were in marsh habitat
dominated with cattails (Typha spp.) or bulrushes (tules)
(Schoenoplectus spp. and Scirpus spp), or both. Neff (1937, p. 78) also
stated that, while cattail and bulrushes were favored nesting
substrates for the species, there was a surprising adaptability in the
nest sites chosen. Vegetation such as barley (Hordeum spp.), mustard
(Brassica nigra), blackberries (Rubus spp.), thistles (Cirsium and
Centaurea spp.), nettles (Urtica sp.), and willows (Salix spp.) were
used as nesting substrate, even when seemingly available cattail and
bulrush marshes were nearby. These observations led Neff to conclude
that marshes were not necessary for the continued existence of the
tricolored blackbird, although he could not determine if there had been
a change in habitat preference during the history of the species (Neff
1937, p. 78).
In recent decades many colonies of breeding tricolored blackbirds
have been found to use nesting substrates such as giant cane (Arundo
donax), safflower (Carthamus tinctorius), tamarisk (Tamarix spp.), mule
fat (Baccharis salicifolia), Fremont cottonwood (Populus fremontii),
California ash (Fraxinus latifolia), Himalayan blackberries (Rubus
discolor), and wheat (Triticum spp.) (Beedy and Hamilton 1999, p. 5).
The species has also been found in silage and grain fields in the San
Joaquin Valley (Collier 1968, pp. 20, 21).
Dairies and feedlots have been recently documented as habitat
components for many tricolored blackbirds. In 1994, approximately 55
percent of all observed breeding colonies were associated with dairies
(Hamilton et al. 1995, pp. 5, 64). In some colonies, water source,
nesting substrate, and foraging area were all available under the
management of a single dairy operation.
Hamilton (1998, p. 218) extensively studied the breeding season
movements of tricolored blackbirds in the Central Valley of California,
from 1994 to 1997. Hamilton (1998, p. 218) concluded from his data that
tricolored blackbirds nest again in the same year at different
localities, a pattern called itinerant breeding. Initiation of nesting
in tricolored blackbirds occurs in late March to early April throughout
California, but primarily in the San Joaquin Valley. Nesting occurs
again in May to June in the Sacramento Valley and foothill rice growing
areas (Hamilton 1998, pp. 223, 224; Beedy and Hamilton 1999, p. 4).
Subsequent nesting efforts for tricolored blackbirds at some colonies
may result in producing as many fledglings as the initial effort, but
the usual nesting success is only a fraction of the initial effort
(Beedy and Hamilton 1999, p. 11).
[[Page 70485]]
Foraging
Tricolored blackbirds rapidly exploit any locally abundant insect
prey, including grasshoppers (Orthoptera), beetles and weevils
(Coleoptera), caddis fly larvae (Trichoptera), moth and butterfly
larvae (Lepidoptera) (Crase and DeHaven 1978, p. 257), dragonfly nymphs
(Odonata), and lakeshore midges (Diptera), as well as grains, snails,
and small clams (Beedy and Hamilton 1999, p. 6). Tricolored blackbird
foraging habitat during all seasons includes dry seasonal pools,
pastures, rice fields, feedlots, dairies, and agricultural fields that
are continuously mowed, such as alfalfa. The species is also known to
forage in other areas, such as grasslands, marsh borders, and scrub,
and saltbrush (Atriplex spp.), but rarely utilizes typically weed free
areas such as vineyards, intensely managed orchards, and row crops
(Beedy and Hamilton 1997, p. 5).
Nesting tricolored blackbirds usually forage within 5 kilometers
(km) (3 miles (mi)) of the breeding colony site (Orians 1961b, p. 299).
However, Beedy and Hamilton (1997, p. 5) observed tricolored blackbirds
foraging up to 13 km (8 mi) from the breeding colony. Orians (1961a, p.
305) explained that the colonial structure of the tricolored blackbird
is very energy demanding when compared to a similar species such as the
red-winged blackbird, due to the large amount of energy expended while
flying to and from distant feeding sites while providing forage for
young. Food that can be rapidly exploited at the foraging site needs to
meet the high energy requirement of the tricolored blackbird. Orians
and Collier (1962, pp. 456-458) stated that because of the tricolored
blackbird's high energy requirement, the species has an unpredictable
breeding distribution and in unfavorable years has lower reproductive
success than the red-winged blackbird. The presence of abundant and
easily available food is a requirement for a successful tricolored
blackbird colony and breeding location, and colony size can vary year
to year depending on food availability and other environmental
conditions (Orians 1961a, p. 308).
Range and Distribution
The tricolored blackbird is largely native to California, where
more than 95 percent of the population occurs. Neff (1937, p. 63)
described the range of the tricolored blackbird as largely endemic to
the lowlands of California, west of the Sierra Nevada, but also
sparsely occurring in southernmost Oregon and northwestern Baja
California. The elevational range of the tricolored blackbird was
documented by Neff (1937, p. 80) as going from sea level in San Diego
and Santa Cruz Counties to about 1,200 meters (m) (3,937 feet (ft)) at
Klamath Lake, Oregon. High-elevation colonies have been found in
California at 1,158 m (3,800 ft) near Tehachapi, Kern County (Collier
1968, pp. 9, 10). DeHaven et al. (1975, p. 171) stated that the overall
geographic range of the species had not changed very much in the past
30 years, and that colonies were still found in southern Oregon through
Shasta County, California, along the coast from Sonoma County,
throughout the Central Valley, and south to northwestern Baja
California, Mexico. Sparse colonies have also been documented in
Washington and Nevada (Beedy and Hamilton 1999, p. 3).
United States
California. Active tricolored blackbird breeding colonies have been
recorded in 46 counties in California since the 1980s, with the largest
colonies being observed in the Central Valley (Beedy and Hamilton 1999,
p. 3). The species currently breeds west of the Cascade Range, into the
foothills east of the Sierra Nevada, north in Honey Lake basin in
Lassen County, and in marshes of the Klamath basin in Siskiyou and
Modoc Counties. The species also breeds from Humboldt to Shasta
Counties, continuing south to southwestern San Bernardino County,
western Riverside County, and western and southern San Diego County
(Beedy and Hamilton 1999, p. 3).
Oregon. The most reoccurring breeding colonies in Oregon occur in
southern Klamath and southern Jackson Counties. A few other isolated
breeding occurrences have been documented in northeastern Multnomah
County, John Day Fossil Beds National Monument in Wheeler County,
Umatilla County, and Lake County in southern Oregon. Tricolored
blackbird breeding colonies in Oregon range from dozens to a few
thousand breeding adults (Beedy and Hamilton 1999, p. 3; Marshall et
al. 2003, pp. 578-580).
Washington. A small breeding colony was reported in Grant County in
1998, the first recorded observation for the State (Beedy and Hamilton
1999, p. 3). Since 1999, the species has been recorded every month,
except during the month of August, in Adams County (Seattle Audubon
Society Web site 2006). A small breeding colony was discovered along
Crab Creek, Grant County in 1998. In 2005, an additional larger colony
was recorded near Texas Lake in Whitman County (Seattle Audubon Society
Web site, 2006).
Nevada. The first recorded breeding colony of tricolored blackbirds
was documented in 1996, in Carson Valley, Douglas County, in western
Nevada (Beedy and Hamilton 1999, p. 3). More recent observations have
found a recurring colony in a small freshwater marsh in the Carson
Valley that is not known to exceed 20 breeding pairs of tricolored
blackbirds per year (Floyd et al. 2006).
Mexico
Baja California. Tricolored blackbirds breed primarily in emergent
marsh from the central and western portions of Baja California Norte,
south to El Rosario, Mexico (Beedy and Hamilton 1999, p. 3; Hamilton
2006). Tricolored blackbird breeding colonies on Baja range from a
handful of breeding adults to a few thousand, with very few birds being
observed in winter months (Erickson 2006).
Winter Range
In the winter, tricolored blackbirds reside within a portion of
their breeding range, with concentrations in coastal areas such as
Monterey, Marin, Sonoma, and Santa Cruz Counties, and in and around the
Sacramento-San Joaquin River Delta in California (Beedy and Hamilton
1999, p. 3). Some small populations may remain during the winter within
Oregon, Nevada, other portions of California, and Baja California,
Mexico (Beedy and Hamilton 1999, p. 3).
Population Studies
Population studies on tricolored blackbirds began with the studies
of Neff, who conducted observations on the species from 1931 through
1936 covering portions of the range (Neff 1937, p. 62). Location and
level of survey effort varied from year to year. Neff (1937, pp. 61-80)
found up to 491,000 nests and an estimated 737,000 breeding birds in
1934 within the Sacramento Valley.
While completing life history studies in Colusa and Yuba Counties,
Orians (1961a, p. 285, 286, 297) located a colony in 1960 with more
than 100,000 nests (estimated 150,000 breeding birds) in Colusa County,
and several other colonies from 1957 through 1960 which contained
nearly 100,000 nests each. Orians (1961a, p. 309) stated that
tricolored blackbirds were in no threat of immediate extinction and
that their ecology led them to be highly adaptable birds.
DeHaven et al. (1975 p. 166) completed a population survey in each
[[Page 70486]]
breeding season (April-June) from 1969 through 1972. DeHaven et al.
(1975) estimated the population size of tricolored blackbird colonies
using either of two methods: (1) Counting the number of breeding birds,
or (2) Counting nests to estimate the number of breeding birds. In 1969
and 1970, the surveys were concentrated in the Central Valley, but
there were also reports from Riverside and Siskiyou Counties (DeHaven
et al. 1975, p. 166). In 1969, an estimated 181,000 breeding birds were
located in the 19 counties surveyed. In 1970, an estimated 84,850
breeding birds were located in the 19 counties surveyed. In 1971,
surveys attempted to include the entire breeding range, except Baja
California, from San Diego to southern Oregon. An estimated 167,540
breeding birds were reported from 24 counties in California and Oregon.
In 1972, an estimated 97,850 breeding birds were reported from 14
counties from the northern San Joaquin valley through to southern
Oregon (DeHaven et al. 1975, pp. 169, 170, 177). DeHaven et al. (1975,
p. 179) concluded the population had declined compared to the surveys
conducted by Neff in the 1930s.
In 1994, the National Audubon Society, CDFG, the Service,
University of California at Davis (UCD), and experienced volunteers
initiated a one-day, rangewide population census in California of the
tricolored blackbird (Beedy and Hamilton 1997, pp. 12, 13). Nearly all
areas of the species' range were surveyed (Hamilton et al. 1995, p. 7).
The survey was conducted from April 22 through April 24, 1994, with the
assumption that the minimum number of birds entering the 1994 breeding
season would be documented (Hamilton et al. 1995, pp. 14, 15). Census
participants located an estimated 324,621 breeding birds across the
range. This number was significantly higher than estimates of between
84,850 to 181,000 breeding birds reported by DeHaven et al. (1975).
In 1997, a CDFG-coordinated population survey was conducted
following the methods in Hamilton et al. (1995) (Beedy and Hamilton
1997, p.13). On April 27, 1997, census participants located an
estimated 217,696 breeding tricolored blackbirds as compared to an
estimated 324,621 breeding birds in 1994.
In 2000, the Service sponsored a population estimate survey, which
was coordinated by UCD and the California Audubon Society between April
21 and 24, 2000 (Hamilton 2000). The 2000 survey attempted to: (1)
Locate all tricolored blackbird colonies throughout their current
(April 21-24, 2000) distribution in California; (2) Estimate their
numbers; and (3) Determine the outcome of their nesting activity
(Hamilton 2000, pp. 7-8). As in past surveys in 1994 and 1997, focus on
a particular date avoided counting birds twice as they moved to
different areas during the breeding season. Approximately 153,995
breeding birds were located throughout California during the April
census (Hamilton 2000, p. 27). Hamilton (2000, p. 8) stated that this
population estimate represented an uneven portion of the species'
breeding range, because intensively farmed agricultural areas in the
Central Valley are seldom surveyed, and as a result, colonies are
likely not located.
In 2004, a survey was conducted in the Central Valley and four
counties outside the Central Valley (Siskiyou, Santa Clara, Monterey,
and Riverside) from April 16 to April 19, 2004 (Green and Edson 2004,
p. 23). The goal of the 2004 survey was to visit all historical
breeding colonies in the Central Valley where 2,000 or more birds were
previously found. Of the 184 historic colony sites surveyed (out of 216
historic records), 28 sites surveyed supported active colonies (Green
and Edson 2004, p. 25). Although no formal breeding population estimate
was made for 2004, Green and Edson (2004, pp. 25, 27) reported that
colony sizes recorded in 2004 were between 5 and 102,000 breeding
adults.
Hamilton (2004, p. 32), using his own data and data collected by
Green and Edson (2004), estimated that 223,069 young fledged from the
entire breeding season in 2004 (Hamilton 2004, p. 39). Approximately
97,733 of the 223,069 fledged from a colony on Delevan National
Wildlife Refuge (NWR) of an estimated 136,000 breeding birds (Hamilton
2004, p. 38). This colony is the largest documented since the 1960s. In
2005, Hamilton and Meese (2006, p. 6), using the same methods as in the
1994, 1997, and 2000 surveys, estimated 260,000 breeding birds in the
population.
Threats Analysis
Section 4 of the Act and its implementing regulations (50 CFR 424)
set forth the procedures for adding species to the Federal list of
endangered and threatened species. A species may be determined to be an
endangered or threatened species due to one or more of the five factors
described in section 4(a)(1) of the Act: (A) Present or threatened
destruction, modification, or curtailment of habitat or range; (B)
Overutilization for commercial, recreational, scientific, or
educational purposes; (C) Disease or predation; (D) Inadequacy of
existing regulatory mechanisms; or (E) Other natural or manmade factors
affecting its continued existence. In making this finding, we evaluated
whether threats to the tricolored blackbird as presented in the
petition and other information available in our files at the time of
the petition review may pose a concern with respect to the species'
survival such that listing under the Act may be warranted. Our
evaluation of these threats is presented below.
For the five-factor threats analysis, we have included the
information submitted by the petitioner in its entirety for each
factor, and then included our evaluation of the information provided by
the petition and our evaluation of other information available to us
regarding threats to the species.
A. Present or Threatened Destruction, Modification, or Curtailment of
the Species' Habitat or Range
Information Provided by the Petitioner
Destruction of Native Habitats
The petitioner claims that loss and degradation of native breeding
habitat for the tricolored blackbird threaten the species and have led
to a significant decline in the overall population size throughout its
range. The petitioner cites the studies conducted in the 1930s (Neff
1937) to support this claim. The population studies conducted by Neff
(1937, p. 77) state that many favorable habitats of the tricolored
blackbird, including emergent vegetation growth, have been destroyed by
reclamation, drainage, dredging, reservoir construction, and clearing
of marshes and canals.
According to the petition, only 560,000 acres (ac) (226,624
hectares (ha)) of the original 4 million ac (1.6 million ha) of
wetlands in the Central Valley still existed by 1939, and by the mid
1980s only 243,000 ac (98,339 ha) of wetlands remained (Beedy and
Hamilton 1997, pp. 10, 11). The petition further states that native
perennial grasslands have been reduced by more than 99 percent in the
Central Valley and surrounding foothills of California (Beedy and
Hamilton 1997, p. 11). The petition claims that the remaining marsh
nesting habitat for tricolored blackbirds has been reduced to small
isolated patches, and these patches support high concentrations of
tricolored blackbird predators (predation is addressed under Factor C,
below).
The petition also discusses the loss of breeding habitat at sites
where colonies once occurred, such as in Yolo County
[[Page 70487]]
during the 1930s. Colonies were not re-located due to little or no
habitat remaining during subsequent studies between 1969 and 1972
(DeHaven et al. 1975, p. 179).
Colony Destruction by Agricultural Activities
The petition cites a white paper and briefing statement (USFWS
2000, p. 1) to claim that tricolored blackbirds nest in grain silage
fields at the same time that forage is harvested for optimum moisture
content. The petition asserts that harvesting of grain silage causes
nest destruction and direct mortality and further claims that this
threatens most of the remaining breeding population of the species. In
addition, the petition cites Beedy and Hamilton (1997, p. 17) to
support the claim that many agricultural areas within the range of the
tricolored blackbird have been converted to urban uses and that the
urbanization of agricultural lands will continue to result in loss of
habitat used by the tricolored blackbird.
The petition states that tricolored blackbirds have been adaptive
in their choice of nesting substrates and have shown an increasing
trend towards use of upland substrates for nesting since the 1930s
(Cook and Toft 2005, p. 75). The petition also states that use of
silage fields at dairies is a relatively recent phenomenon and is a
primary nest site selection substrate (Beedy and Hamilton 1997, pp. 4,
18; Beedy and Hamilton 1999, p. 5).
The petition provides data compiled from various surveys that
provide examples of recent breeding failures because of silage harvest.
The petition concedes that the list is not complete, and states that
the concentration of most of the tricolored blackbird reproductive
effort into a few large colonies that are selecting grain silage as a
nesting substrate has greatly increased the risk of extinction should
the annual destruction of such a large proportion of nests continue
unabated (Cook and Toft 2005, p. 85).
Destruction of Other Suitable Upland Breeding Substrates and
Surrounding Habitats
The petition claims that more recent important nesting substrates
include agricultural fields (especially grain silage) and Himalayan
blackberry (DeHaven et al. 1975, pp. 171, 172; Hamilton et al. 1995, p.
25; Cook 1996, pp. 23, 24). The petition claims that the lack of
protection and loss of non-native nesting substrates such as Himalayan
blackberry, thistle, and prickly lettuce are a threat to the tricolored
blackbird. These non-native nesting substrates occur on private
property and are often subject to removal. The petition states that
Himalayan blackberry supports the highest density of nesting tricolored
blackbirds among all other substrates, and that reproductive success is
higher than in other commonly used substrates such as emergent marsh
and silage (Cook and Toft 2005, pp. 85-86).
Curtailment of the Species' Range
The petitioner contends that the loss of wetland and grassland
habitats has led to tricolored blackbirds remaining in a few large but
isolated population centers. However, the petitioner does not claim
that the range of the species has declined significantly. The petition
claims that the species is found throughout its former range, including
small populations in Washington, Oregon, and Nevada, but that few if
any reports of tricolored blackbird nesting have been confirmed since
1999.
Evaluation of Information in the Petition and Information Available to
Us at the Time of Petition Review
Destruction of Native Habitats
The petitioner cited Neff (1937, p. 77) and Beedy and Hamilton
(1997, pp. 10, 11) to support the claim that there has been significant
native habitat loss for the tricolored blackbird. The petition claims
this is a threat to the species and that by 1939, 86 percent of native
marsh habitat had been reduced in the Central Valley. We agree with the
petitioner that wetland loss has occurred for many decades in the
Central Valley of California, resulting in loss of tricolored blackbird
habitat. However, our review of the literature found that while Neff
(1937, pp. 78-79) does discuss that habitat loss had occurred prior to
and during his studies from 1931 to 1936, he did state that all of the
threats to the species during his studies, such as human activities,
predators, weather, or other factors, had only minimal impact on the
species. Further, Neff (1937 p. 78) stated that tricolored blackbirds
showed surprising adaptability in their choice of nesting substrates,
even when seemingly favorable native wetland marshes were available,
and that tricolored blackbirds were nesting in almost every county in
which they had nested during the period 40-70 years prior to his
studies (approximately 1867 to 1897).
Furthermore, Orians (1961a, p. 309) stated that Neff's (1937, p.
62) studies were initiated due to the concern that tricolored
blackbirds may not adapt well to conditions such as water drainage and
conversion of grasslands to cultivation. Orians (1961a, pp. 309, 310)
stated that tricolored blackbirds were not in danger of immediate
extinction, but that they were highly adaptable in their choice of
nesting substrate and in utilizing the abundant food supply of insects
in agricultural lands of the California Central Valley. Because of the
species' apparent ability to utilize a range of habitat types, we do
not believe that historic habitat losses have been demonstrated to be a
substantial threat to the species.
DeHaven et al. (1975, pp. 175, 176, 179) also state that suitable
nesting habitat for the tricolored blackbird had been lost in some
local areas. However, they also state that these local losses in
habitat have not contributed significantly to any overall population
decline of the species, and that tricolored blackbirds leave many
apparently suitable nesting sites unused, likely because of yearly food
availability and water supply and other potentially unknown factors.
DeHaven et al. (1975, pp. 166-180) stated that more research was needed
to help isolate a cause for the apparent decline from 1969 to 1972, as
compared to Neff's (1937, pp. 66, 67) population estimates from 1931 to
1936. Because no complete surveys were conducted between 1937 and 1969,
it is difficult to draw conclusions. Based on the limited number of
surveys during this time period, it is possible that no decline did
occur, and that population numbers are within a range of variability
that would be expected for this species.
As stated earlier in the Population Studies section, status surveys
for tricolored blackbirds began with the studies of Neff from 1931 to
1936 (Neff 1937, pp. 61-81), where Neff estimated between 95,000 and
737,000 breeding birds for the 5-year timeframe. DeHaven et al. (1975,
pp. 166-180) estimated a rangewide population of between 84,850 and
181,000 breeding birds between 1969 and 1972. More recent surveys
estimated 324,621 breeding birds in 1994; 217,696 in 1997; 162,000 in
2000; and 260,000 in 2005. Based on these population estimates, we do
not agree with the petitioner's assertion that the population is in
decline. That relatively low numbers were recorded since Neff's (1937)
high estimate of 737,000 birds in the 1930s does not in our view
provide substantial information that the species may warrant listing
because of the uncertainty of Neff's estimating procedures and recent
comparable studies show the species to be stable or increasing since
the 1970s.
[[Page 70488]]
Colony Destruction by Agricultural Activities
The petition cites a Service white paper and briefing statement
(Service 2000) stating that harvesting of grain silage causes nest
destruction and direct mortality, which threatens most of the remaining
breeding population of the species. We agree that active colonies
nesting in silage should be protected, and that loss of tricolored
blackbirds and reduction of nesting success occurs and may cause
localized declines. The white paper and briefing statement was
developed to inform and provide recommendations to Service management
for managing tricolored blackbird use of dairy silage as a nesting
substrate. The paper outlined concerns of using silage buyouts as a
long-term solution to tricolored blackbird conservation. However, no
information provided by the petitioners or other information otherwise
available to us including the white paper or information cited in the
paper (i.e. DeHaven 2000) suggests that silage harvest has or will
contribute to a rangewide population decline. Population numbers since
the 1970s, as discussed above, appear to be somewhat stable. Tricolored
blackbirds may breed more than one time in the breeding season if a
prior breeding effort failed (Hamilton 1998, pp. 223, 224). Although
the subsequent breeding effort may be smaller than the initial effort
(Beedy and Hamilton 1999, p. 11), the ability to re-nest probably
mitigates the occasional loss of nests with silage cutting. Hamilton
(2004, p. 43) also stated that the claim of declines in the tricolored
blackbird population due to the harvesting of silage is not based upon
a complete analysis of existing data.
Destruction of Other Suitable Upland Breeding Substrates and
Surrounding Habitats
The petition cites Cook and Toft (2005, pp. 85, 86) as stating that
Himalayan blackberry supports the highest density of tricolored
blackbird nesting among all other substrates, and that therefore lack
of protection of this habitat is a threat to the tricolored blackbird.
We agree that tricolored blackbirds may nest in non-native substrates
such as Himalayan blackberry, thistles, and prickly lettuce, as stated
by the petition. However, we have no information and the petitioner
provided no information to suggest that the lack of protection of non-
native substrates such as Himalayan blackberry is a threat to the
continued existence of the tricolored blackbird. Again, as stated
above, the most recent surveys estimate the tricolored blackbird
population has increased from 162,000 to 260,000 breeding birds since
2000, and the number of birds appear to be consistent with, or higher
than, the numbers of birds found in the 1970s. Further, no information
is available to suggest that breeding habitat should be considered
limiting, or that its loss should be considered a substantial threat.
For these reasons, we reject the petitioner's assertions that lack of
protection for breeding habitat should be considered a threat.
Range and Distribution
The petition does not specifically claim that a reduction in range
has occurred for the species, but it does state that few if any
breeding reports outside of California have been confirmed since 1999.
We reviewed currently available information on tricolored blackbird
breeding from Washington, Oregon, and Nevada, and found that this
information supports the contention that the species continues to breed
in these areas and documents new areas where it has been found between
2003 and 2006 (Marshall et al. 2003, pp. 578-580; Floyd et al. 2006;
Seattle Audubon Society Web site, 2006). Based on this recent
information we disagree with the petitioner that few if any breeding
reports outside of California have been confirmed since 1999, but that
the most current information shows new breeding colonies in all three
states.
Summary of Factor A
To summarize Factor A, information included in the petition and
information otherwise available to us demonstrate that destruction of
native habitats, direct nest loss and mortality caused by agricultural
activities, and destruction of other suitable breeding habitats has
occurred and may continue to impact the local abundance and viability
of tricolored blackbirds. Loss of wetlands has occurred in the Central
Valley of California in tricolored blackbird habitat for many decades.
However, the population has increased in recent survey years and
appears to be stable since the 1970s. The petition has presented no
information that suggests that the habitat loss experienced is having
an impact on the population levels of the tricolored blackbird.
Additionally, the harvesting of silage during the tricolored blackbird
breeding period can have localized negative impacts on species habitat
and populations due to direct mortality and nest destruction. However,
we currently have no information and the petition provided no
information on how the loss of a local breeding effort affects the
population in subsequent years, or to support a determination that
silage harvesting is a substantial risk to the rangewide population and
continued existence of the tricolored blackbird. The species is found
throughout the majority of its historical range, with additional new
breeding populations documented in Washington, Oregon, and Nevada.
Therefore, we find that the petition and other information otherwise
available to us does not contain substantial scientific or commercial
information indicating that the continued existence of the species is
threatened by the present or threatened destruction, modification, or
curtailment of the species' habitat or range.
B. Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
Information Provided by the Petitioner
The petition claims that a history of widespread persecution of
blackbird species has likely contributed to a decline in the tricolored
blackbird. The petition cites Neff (1942, pp. 46, 47) who stated that
in 1928 and 1929, market hunting for blackbirds in the Central Valley
of California became a thriving business and a market was created in
large cities by Italian produce firms. Market hunters killed thousands
of blackbirds; it was reported that one group of market hunters shipped
nearly 400,000 blackbirds from the Sacramento Valley in five seasons
(Neff 1942, pp. 46). Market hunting started to decrease by 1936 and
1937, with an estimated 88,000 birds being shipped (Neff 1942, pp. 47).
The petition also cites Neff (1942, pp. 46, 47) as stating that
numerous blackbirds were reportedly shot by ranchers, used by people as
target practice, and poisoned to control damage to crops. The
petitioners state that these killings were a source of high adult
mortality. The petitioners also state that poisoning of thousands of
blackbird species to control rice crop damage in the Central Valley of
California continued until the 1960s (Beedy and Hamilton 1997, p. 18).
The petition states that due to improved harvesting methods, rice
varieties that ripen faster, and fewer individual blackbirds,
extermination programs have ceased; however, the historic occurrence of
blackbird poisoning has likely contributed to the species' population
decline (Beedy and Hamilton 1997, p. 18).
[[Page 70489]]
Evaluation of Information in the Petition and Information Available to
Us at the Time of Petition Review
We agree that tricolored blackbirds were deliberately killed
historically for market use, sport hunting, or protection of crops by
use of poisons or guns; however, we are not aware of a current market,
sport hunting or protection of crops by the use of poison on the
tricolored blackbird. No information was provided by the petitioners or
was available to us that documents any historic or current information
describing how poisoning or market hunting may have contributed to the
overall decline of the species' population size or reduction in its
range. Therefore, we find that the petition does not contain
substantial scientific or commercial information to indicate that the
tricolored blackbird is threatened by overutilization for commercial,
recreational, scientific, or educational purposes.
C. Disease or Predation
Information Provided by the Petitioner
The petition cites several papers (Hamilton et al. 1995, p. 21;
Beedy and Hamilton 1997, p. 10; Hamilton 2000, p. 14) that describe
predation as major cause of large-scale nesting failures in many
tricolored blackbird colonies, especially those colonies that nest in
native emergent marsh. The petition cites Hamilton et al. (1995, pp.
21, 35) and Hamilton (2000, pp. 13, 14) to claim that black-crowned
night-heron and raccoon predation on tricolored blackbird colonies in
marshes can destroy all or the majority of nests within such colonies,
which results in nest failure of the entire colony. The petition states
that tricolored blackbirds nesting at Kern NWR in Kern County and the
Maxwell I and II colonies in Colusa County failed due to black-crowned
night-heron predation. The petitioners also state that black-crowned
night-heron predation on the tricolored blackbird is of special concern
at National Wildlife Refuges, because the refuges are becoming more
important nesting sites for black-crowned night-herons and tricolored
blackbirds as private lands are converted to other uses, and as grain
silage fields may be harvested during the tricolored blackbird nesting
season. The petition cites Cook and Toft (2005, pp. 80-82) to claim
that tricolored blackbird reproductive success was much lower in native
emergent marsh than in any other nesting substrate, except for silage
that was lost to harvesting operations.
The petition also cites a long list of historic, native predators
that may have preyed upon tricolored blackbirds, and claims there have
been recent reports of predation on tricolored blackbird colonies by
feral cats (Felis catus) (Beedy and Hamilton 1997, p. 17). The petition
also states that tricolored blackbirds are not aggressive towards
predators and will sit silently instead of attacking, unlike the
behavior of red-winged blackbirds (Beedy and Hamilton 1997, p. 17,
Beedy and Hamilton 1999, p. 12).
The petition does not discuss or provide any information on how
disease threatens the tricolored blackbird.
Evaluation of Information in the Petition and Information Available to
Us at the Time of Petition Review
The petition infers from Hamilton et al. (1999) that reproductive
success of tricolored blackbirds in cattail marshes is low because of
the high rate of predation that this nesting substrate endures due to
high concentration of predators such as raccoons and black-crowned
night-herons. Hamilton et al. (1999, p. 12) stated that expansion of
large cattail nesting areas for tricolored blackbirds should be
avoided, due to high predation of colonies in this type of nesting
substrate. However, Hamilton (2000 p. 20) withdrew the previous
statement made in 1999 due to observations made in 2000 of low or
absent black-crowned night-heron predation on other tricolored
blackbird colonies nesting in cattails. In 2000, Hamilton (2000, p. 28)
observed large tricolored blackbird colonies in cattails which were not
preyed upon by black-crowned night-herons. The large colonies include
the two colonies on Delevan NWR that contained approximately 37,000
breeding adults and produced approximately 34,000 successful
fledglings. In 2004 at Delevan NWR in Colusa County, a large colony
(approximately 135,000 breeding adults) successfully nested in a
cattail marsh, producing approximately 97,000 fledglings (Hamilton
2004, p. 35). While some predation probably occurs at all tricolored
blackbird colonies, there is insufficient information to suggest or
conclude that predation on nests in cattail marshes is a threat at the
population level.
The petitioners cited an example that tricolored blackbirds nesting
at Kern NWR in Kern County and at Maxwell I and II in Colusa County
failed due to black-crowned night-heron predation. We presume that the
petitioners used Hamilton (2000, pp. 28, 29) for the Maxwell example,
since no reference was given. The data provided by Hamilton (2000, p.
28) indicate the Maxwell I nesting site produced approximately 1,199
successful fledglings from about 5,000 breeding adults, while the
Maxwell II nesting site only produced 38 successful fledglings from
about 2,000 breeding adult tricolored blackbirds. No information was
provided or available to determine why the fledgling rate at Maxwell II
was low. We also could not determine what documentation the petitioners
used to support their claim that a colony at Kern NWR failed due to
predation. According to DeHaven (2000, pp. 17, 18), predation is
reported by researchers about as frequently in the 1990s as it was in
the 1970s, and it is not known if the losses to tricolored blackbird
colonies from predation are within a historical and normal range that
would be expected of a colonial nesting species.
Payne (1969, p. 26) states that the loss to any one breeding effort
of a tricolored blackbird colony may be reduced due to the species'
dense colony structure; a colony is likely to occur within the
territory of only one predaceous raptor. Although tricolored blackbirds
have demonstrated that they are not aggressive defenders against
predators, there is no information available to us or submitted by the
petitioner that shows that lack of aggression towards predators may
threaten the continued existence of the tricolored blackbird.
The petitioner cited Beedy and Hamilton (1997, p. 17) as stating
that predation on tricolored blackbird nests by feral cats is a recent
phenomenon. We found that Beedy and Hamilton (1997, p. 17) cited Payne
(1969, p. 25) who reported predation of tricolored blackbirds by feral
cats. Payne (1969, p. 25) states that dozens of tricolored blackbird
adults were found dead around a marsh in Marysville, California, and
appeared to have been killed by numerous feral cats. While the Service
agrees that predation on the species' nests by feral cats is a more
recent occurrence than other predation reported in the early 1900s,
there is no current evidence available to us or supplied by the
petitioner to suggest that feral cat predation is significant range
wide, or a threat to the continued existence of the tricolored
blackbird.
Summary of Factor C
To summarize factor C, information provided in the petition and
other available information suggests that predation on tricolored
blackbird colonies does occur. Predation on tricolored blackbird
colonies nesting in cattail marshes by black-crowned night-herons has
been documented. While the Service agrees that predation occurrences
may be the potential cause of some nesting failures, especially in
[[Page 70490]]
cattail marshes, evidence also demonstrates that tricolored blackbirds
can breed successfully in cattail marshes. There is no evidence that
predation has increased above natural levels and is often localized in
nature. We are not aware of any information indicating that predation
has caused a reduction in the range or population size of the species,
or that a reduction in the population of this species is likely to
occur in the future due to predation. Therefore, we find that the
petition does not contain substantial scientific or commercial
information to document disease or predation may be a factor that
threatens the tricolored blackbird.
D. The Inadequacy of Existing Regulatory Mechanisms
Information Provided by the Petitioner
The petition claims that the tricolored blackbird is not protected
by existing regulatory mechanisms. The petition stated that the
tricolored blackbird is considered a non-game bird of management
concern by the Service. The petition also stated that the tricolored
blackbird is considered a species of special concern by the CDFG.
Additionally, the petition states that the tricolored blackbird is not
listed under the Act or the California Endangered Species Act
(California Fish and Game Code section 2070 et seq). The petition
claims that current designations do not provide specific legal
protection to the species aside from the requirement that a project may
trigger California Environmental Quality Act (CEQA) review where the
impacts of the proposed action on the species must be analyzed. Actions
that do not trigger CEQA would not require review. The petition also
claims CEQA's mandates for environmental protection have not been
implemented to protect the tricolored blackbird.
The petition states that the Migratory Bird Treaty Act (MBTA)
should afford the species protection; however, the petition further
states that the statute is rarely if ever enforced against private
landowner violators, and that enforcement agencies have turned a
``blind eye'' to annual violations of the MBTA by private landowners.
The petition states that the statute strictly prohibits all ``taking''
(to ``pursue, hunt, shoot, wound, kill, capture, or collect,'' or
attempt to do so) of migratory birds unless authorized by a permit
issued under Department of the Interior regulations (16 U.S.C. 703) and
under 50 CFR 10.12. The petition claims that private property owners
who destroy tricolored blackbird nests are in clear violation of the
MBTA and its implementing regulations.
Additionally, the petition claims that private landowners with
dairies or other commercial agricultural operations on their property
are in violation of the California Business and Professions Code
Section 17200, and the MBTA. The petition states that the code defines
``unfair competition'' to include ``unlawful, unfair or fraudulent
business practice and unfair, deceptive, untrue or misleading
advertising.'' A business practice constitutes unfair competition if it
is forbidden by any law, whether civil or criminal, whether Federal,
State, or municipal, or whether statutory, regulatory, or court-made.
The petition claims that private business owners who are destroying
tricolored blackbird nests are vulnerable to enforcement actions under
both the MBTA and the California Business and Professions code.
Evaluation of Information in the Petition and Information Available to
Us at the Time of Petition Review
The tricolored blackbird is considered a U.S. Fish and Wildlife
Service Bird of Conservation Concern (USFWS 2002). In general, species
are classified as such because of (1) Documented or apparent population
declines, (2) Small or restricted population, or (3) Dependence on
restricted or vulnerable habitats. This designation is a result of
mandates required through the Fish and Wildlife Conservation Act, which
in part requires the Service to identify non-game migratory bird
species that, without additional conservation actions, are likely to
become candidates for listing under the Act. While all of the bird
species included in the list are priorities for conservation action,
the list makes no finding with regard to whether they warrant
consideration for federal listing. The goal is to prevent or remove the
need for additional listings by implementing proactive management and
conservation actions.
In May 1990, the CDFG added the tricolored blackbird to its species
of concern list. In general CDFG classifies species as such because
they (1) Are declining at a rate that could result in listing, or (2)
historically occurred in low numbers and known threats to their
persistence currently exist. This classification offers no legal
protection in itself, but encourages consideration of the species in
impact analyses, mitigation planning, and other environmental
documentation (Beedy et al. 1991, p. 5).
Local governments are typically the lead agency for conducting CEQA
review of projects to convert native vegetation; thus, CDFG considers
an environmental document prepared by the lead agency. CDFG considers
potential impacts of the proposed project and provides information to
the lead agency about possible impacts to wildlife species and habitat.
CDFG can provide advisory recommendations for avoiding, minimizing, and
mitigating impacts of the project. Recommended measures to reduce or
avoid impacts do not become mandatory, unless adopted by the lead
agency. Changes in agricultural uses, including those that may result
in impacts to tricolored blackbirds, do not typically trigger CEQA
requirements or allow for CDFG review (Gustafson and Steele 2004, p.
31).
The Migratory Bird Treaty Act implements various treaties and
conventions between the United States and Canada, Japan, Mexico, and
the former Soviet Union for the protection of migratory birds. Under
the MBTA, taking, killing or possessing migratory birds is unlawful.
Unless permitted by regulations, the MBTA provides that it is unlawful
to pursue, hunt, take, capture or kill; attempt to take, capture, or
kill; possess; offer to or sell, barter, purchase, or deliver; or cause
to be shipped, exported, imported, transported, carried, or received,
any migratory bird, part, nest, egg or product, manufactured or not (16
U.S.C. 703). According to the MBTA, a person, association, partnership,
or corporation that violates the MBTA or its regulations is guilty of a
misdemeanor and subject to a fine of up to $15,000, jail up to 6
months, or both. Anyone who knowingly takes a migratory bird and
intends to, offers to, or actually sells or barters the bird is guilty
of a felony, with fines up to $2,000, jail up to 2 years, or both (16
U.S.C. 707).
Historically for the tricolored blackbird, the majority of breeding
occurred in marshes and blackberry thickets. More recently, the species
may nest in the grain silage fields associated with diaries. These
grain silage fields are often harvested (when moisture content of the
forage is optimal) while nesting species are still present (DeHaven
2000, p. 1). The Service agrees with the petitioner that harvesting of
silage while the species is still nesting would be a violation of the
MBTA if eggs and young are destroyed. We pursue investigation of such
MBTA violations as we are made aware of their occurrence.
As stated in the petition, the MBTA is the current Federal
regulatory mechanism in place to protect the tricolored blackbird
throughout its range in the United States. The petition claims that the
Service turns a ``blind eye'' to
[[Page 70491]]
violations of the MBTA. We are unaware of, and were not provided by the
petitioners, with information that documents lack of enforcement of
specific violations under the MBTA. Therefore, we believe that the MBTA
provides protections for the species.
In an effort to conserve and protect the tricolored blackbird, the
Service and CDFG have been cooperating with public and private
stakeholders to address and prevent violations of the MBTA and CEQA.
The petition acknowledges these efforts and cites a 2000 example of
Tevelde Farm in which the agencies arranged to compensate the farm to
delay harvesting of silage to allow approximately 20,000 tricolored
blackbirds to fledge. The Service and CDFG have been funding private
landowners for purchase of silage crops or delay of harvesting
activities since 1993 to avoid taking of nesting tricolored blackbirds
in silage and to enhance reproductive success. The Service recognizes
that these silage purchases or reimbursements for delay of harvest are
not long-term solutions, and will be used as a short-term approach
until a long-term management strategy can be devised to increase
protection of the tricolored blackbird.
Summary of Factor D
To summarize Factor D, existing Federal and State regulations
currently provide protection for the tricolored blackbird through the
Federal Migratory Bird Treaty Act and CEQA review process. The
petitioners only provide speculation on the lack of regulatory
enforcement of the MBTA and CEQA and do not mention specific instances
where these Acts were not enforced. Further, there is no evidence that
lack of regulatory mechanisms is causing a population decline. Due to
this lack of information, we are unable to determine that the
inadequacy of existing regulatory mechanisms has led to reduction in
the population size across all or within the range of the species, or
that a reduction in the population of this species is likely to occur
in the future. Therefore, we find that the petition does not present
substantial scientific or commercial information that lack of
regulatory mechanisms may present a threat to the tricolored blackbird.
E. Other Natural or Manmade Factors Affecting the Species' Continued
Existence
Information Provided by the Petitioner
Chemical Contaminants
The petition claims that chemical contaminants are a threat to
birds, including the tricolored blackbird, and those contaminants can
cause mortality and nesting failures. While the petition acknowledges
that the ``link between environmental contaminants and nesting failure
of tricolor[ed]s is largely unstudied,'' the petition claims that some
mortality of tricolored blackbirds has been documented due to chemical
toxicity and this source of mortality could become more substantial if
tricolored blackbird populations continue to decline. Citing Beedy and
Hayworth (1992, pp. 33-35), the petition describes a complete nesting
failure of approximately 50,000 tricolored blackbirds, at Kesterson
Reservoir in Merced County in 1986. The petition also cites Beedy and
Hayworth (1992, pp. 33-35), who collected dead nestlings, of which some
had club feet, along with other species of birds that had similar
deformities, and sampled tricolored blackbird nestlings and found them
to have higher concentration of selenium in their livers than that of
red-winged blackbirds sampled at a nearby location. The petition cites
Beedy and Hamilton (1997, pp. 18, 19) who stated that the suspected
cause of tricolored blackbird nestling deaths in 1986 was from selenium
contamination.
The petition further cites Beedy and Hamilton (1999, p. 18):
Reporting biologist William J. Hamilton III personally observed a
tricolored blackbird colony that failed to hatch due to mosquito
abatement spraying in Kern County. The petition also cites the
California Department of Pesticide Regulation (CDPR) data (CDPR Web
site data 2002) detailing types and quantities of chemicals used in
Sacramento, San Joaquin, Merced, Fresno, and Tulare Counties. The
petition cites EXOTOXNET (2004) to describe which chemicals are toxic
to birds in general. The petition additionally states that although
tricolored blackbirds were not studied directly, many of the chemicals
listed by the CDPR data are highly toxic to birds and are used within
the known breeding range of the species.
Evaluation of Information in the Petition and Information Available to
Us at the Time of Petition Review
Beedy and Hayworth (1992, p. 42) describe that in April 1986,
approximately 47,000 tricolored blackbirds tried to nest at Kesterson
Reservoir. Surveys were conducted from April 18 to 23, 1986, of 162
tricolored blackbird nests. The study found that 84.6 percent of those
nests were either empty or contained addled eggs or dead chicks, and
266 additional chicks were found dead on levee roads. Only 100 birds
were fledged from the Kesterson Reservoir colony, which suggests a near
nesting failure in the 1986 breeding season. Some of the dead nestlings
from 1986, along with dead nestlings from further studies in 1987, were
examined for deformities and their livers were screened for toxins, and
some of the nestlings from both years were determined to have club feet
and high levels of selenium in their livers. Beedy and Hayworth (1992,
pp. 41, 42) state that more research was needed to determine if
selenium contamination was the reason of nestling mortality, and if the
nesting failures observed were an isolated incident or a widespread
general decline of the tricolored blackbird, since the cause and
magnitude of nestling mortality vary tremendously between colonies.
Additionally, in 1986, the U.S. Department of the Interior decided to
close the San Luis Drain, so selenium and salt no longer concentrate at
Kesterson, and tricolored blackbirds no longer nest there. Aside from
the nesting failure due to the potential selenium contamination in
1986, we were provided no information in the petition nor have we
received any other information of other potential selenium-related
nesting failures in tricolored blackbirds or any information supporting
the idea that selenium contamination is currently a threat to the
tricolored blackbird. There also was no information provided by the
petition or otherwise available that describes what effect the nesting
failure at Kesterson had on the tricolored blackbird population in 1986
or subsequent nesting seasons.
The petition did not provide, and we are not aware of, any
information or data to support the observation William J. Hamilton III
made in Kern County of a complete nesting failure due to the spraying
of mosquito abatement. We are not aware of any information or data that
documents this nesting failure or whether the nesting failure was due
to chemical contamination or other factors. While providing information
on pesticide use in five counties in California from the CDPR, the
petition did not provide information beyond speculation regarding the
effects of these chemicals on the tricolored blackbird. Hamilton et al.
(1995, p. 38) stated that limited evidence shows that chemical use in
agricultural areas causes some direct mortality, but the toxins do not
seem to be creating a serious problem for tricolored blackbirds.
Hamilton et al. (1995, p. 38) go on to state that there is no evidence
to show that mortality caused by
[[Page 70492]]
agricultural chemical contamination has depressed tricolored blackbird
numbers below a carrying capacity in any year. Hamilton (2000, p. 20)
stated that there was no documented evidence, since the work of Beedy
and Hayworth (1992), that toxic contaminants have adversely affected
the tricolored blackbird, and those instances provided by the
petitioners as documentation of nest failure due to chemical toxicity
were not substantiated.
Summary of Factor E
To summarize factor E, we agree that high selenium concentrations
have been documented in some of the dead nestlings at Kesterson
Reservoir. However, whether the selenium toxicosis was the cause of
death of these tricolored blackbird nestlings or cause for the complete
nesting failure observed in 1986, or from other factors, is still
unknown. No information was provided suggesting that there are ongoing
dieoffs such as occurred in 1986. In addition, neither the petition nor
other available information provides anything more than speculation on
the types and magnitudes of effects these chemicals may have on the
tricolored blackbird. Due to this lack of information, we are unable to
determine that use of toxic chemicals within the range of the species
has led to reduction in the population size of the species, or that a
reduction in the population of this species is likely to occur in the
future. Therefore, we find the petition does not contain substantial
scientific or commercial information that other natural or manmade
factors may be a factor threatening the continued existence of the
tricolored blackbird.
Finding
We evaluated each of the five listing factors individually, and
because the threats to the tricolored blackbird are not mutually
exclusive, we also evaluated the collective effect of these threats.
The petition focused on all five listing factors. We have reviewed the
petition and supporting literature, as well as other information in our
files on the tricolored blackbird. After our review we find that the
petition did not present substantial information that indicates
rangewide declines, a substantial reduction in population numbers, or
substantiated threats to existing populations that rise to the level
that would indicate the listing of the tricolored blackbird is
warranted or likely to become so in the foreseeable future. Threats to
the tricolored blackbird, as described by the petition, included loss
of native habitats, agricultural activities causing nest destruction
and direct mortality of birds, destruction of other suitable breeding
substrates and surrounding habitats, overutilization of the species,
predation, lack of existing regulatory mechanisms, and chemical
contamination.
While these threats may affect local populations of tricolored
blackbirds, the information provided in the petition was speculative in
nature. The petition did not provide specific information to document
the degree that the species has been affected by these threats, or that
these threats have led to a significant decline in the range or
distribution of the species or are likely to do so in the future.
Surveys conducted for the tricolored blackbird that we are aware of
and that were discussed in the petitioner's information did not use a
consistent level of effort in surveying and the petitioners did not
base their conclusion on the most current population information
available. Therefore, population and distribution trends have varied
throughout survey years due to survey methods in addition to the likely
natural population fluctuations. At present the most recent studies
indicate that, since 2000, the rangewide population of tricolored
blackbirds has increased regardless of any potential habitat loss,
predation, or chemical contamination.
We have reviewed the petition and supporting information provided
with the petition and evaluated that information in relation to other
pertinent literature and information available to us at the time of the
petition review. Based on this review and evaluation, we find that the
petition and other available information does not present substantial
information demonstrating that listing the tricolored blackbird as
threatened or endangered may be warranted at this time. We encourage
interested parties to continue to gather data that will assist with the
conservation of the tricolored blackbird.
References Cited
A complete list of all references cited herein is available, upon
request, from the Sacramento Fish and Wildlife Office (see ADDRESSES).
Author
The primary authors of this notice are staff of Sacramento Fish and
Wildlife Office, U.S. Fish and Wildlife Service, 2800 Cottage Way,
Sacramento, CA 95825.
Authority
The authority for this action is the Endangered Species Act of
1973, as amended (16 U.S.C. 1531 et seq.).
Dated: November 28, 2006.
Kenneth Stansell,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. E6-20547 Filed 12-4-06; 8:45 am]
BILLING CODE 4310-55-P